Abstract

The results of this program indicate there is scope to increase the size and returns to the community of the Tasmanian urchin fishery. This would include husbandry of sheltered coastal reef areas where there is an over abundance of urchins resulting in 'barren' areas. Urchin barren areas presently may make up to twenty five percent of all sheltered coastal reef areas between Coles Bay on Tasmania's east coast
and Southport in the south. Urchin husbandry will not occur through the current
management regime and requires a coordinated effort involving processors and divers.
Although small, the sea urchin fishery is one of Tasmania's most labour intensive, with a current ratio of two to four processing employees to each of the fulltime divers. Management of the current fishery is minimal. Consequently, there is declining availability of premium grade roe and the harvest season is short, which results in minimal returns to all sectors and prevents the fishery realising its full
potential.
In many coastal reef areas, 'urchin barrens' are evidenced with reduced availability of preferred foods, including the important native string kelp Macrocystis pyrifera. Denied sufficient food, large colonies of sea urchins have minimal roe weights making their harvest unprofitable. At the same time, our observations indicate they are devastating algal growth in the coastal zone to the detriment of other marine species and the coastal ecosystem.
There is an urgent need to develop cost-effective, commercial enhancement
techniques for these key areas which will restore biological balance and maximise the fishery's value and employment potential by increasing both roe weight and roe quality. .
The main aim of this research program was to determine the potential for culling urchins in some areas and encouraging the return of appropriate seaweed species. Tasmanian Sea Urchin Developments used two widely-separated sub-tidal experimental lease areas. The first, at Meredith Point on the east coast and the second, at Hope Island on the south coast. Both sites have been subject to some overgrazing by urchins.
At Meredith Point, the study area was divided into plots containing urchins at three densities: artificially enhanced, continually harvested and control (undisturbed). Urchin roe condition increased in the low urchin density areas relative
to the high and control over a two year period. Thinning of urchin densities in one area that had been a barren resulted in a doubling of roe recovery. At Hope. Island, preliminary short-term trial clearings of urchin from barrens resulted in little recovery of macroalgal vegetation. It was postulated that limpets may be an additional herbivore controlling vegetation so the major manipulation experiment conducted there, was to determine if urchins were the principal herbivore. After two years, vegetation returned to urchin cleared areas but not limpet cleared areas. Urchins were thus determined to be the principal herbivore. Revegetation was augmented by transplanting M. pyrifera plants to the site and reestablishment of algal forests has been successful. '
Supplementary programs were conducted on gonad condition, urchin movement, aging of urchins, kelp transplants and surveys of remote sites. Monitoring of gonad condition demonstrated a regular seasonality to reproduction with optimum roe recovery from September to December. However, the peak of the season and the extent of the season varied from year to year, and from site to site. This may be due to variation in factors of light and nutrient availability and their effects on macroalgae, the primary dietary item. Male urchin had higher quality roe (white-yellow, fine
texture). Quality also varied with age and size of the urchin. Larger, older urchin had
poorer quality roe.
Movement of urchins was investigated because an assumption of the manipulation experiments was that movement was negligible. Movement was found to be minimal and seasonal. Most activity was observed from January to July. At Meredith Point, movement was so small that transplanted urchins released from bags and bins did not move far from their release point resulting in localized concentrations of urchins and the formation of small 'barren' areas.
Tetracycline labelling of teeth showed slow growth rates at both sites, with reproductive maturity being attained at 5-1 0 years of age. This result was a t odds with aging of urchins using marginal increment analysis of teeth, the results of which were ambguous however.
Low recruitment rates, estimated at between 0.3 and 1.0 urchin/mz/yr a t the two research sites, indicate reef areas may be harvested every 2 to 9 years. Observations by urchin diver's and those of the principal investigator suggest low recruitment rates hold true for many areas outside the study areas indicating a precautionary approach to management strategies.
Experimental re-vegetation of M. pyrifera using spores was sporadically successful, possibly dependent on conditions when cultivated spores were out-planted, thus only possible at certain times of the year. Transplanting of juvenile M. pyrifera plants was successful with beds re-established a t Hope Island, Stapleton Point and Oakharnpton Bay.
Surveys of urchins at King Island show there is potential for an urchin industry on the island and may be worth further investigation.
Further research and development is indicated for:
1 ) Best resource management options.
2) Re-seeding reefs or cultivation with preferred urchins for example: white
shells, males.
3) Recruitment and growth rates.
4) Coordinated marketing of product to improve profitability.